The impetus for the nation-wide study of SDI (Selective Dissemination of Information) came from the desire to learn more about the options available for the application of the SDI concept prior to decisions about its possible use in Air Force research and development activities. For this purpose, data on user populations, literature coverage, methods of establishing and maintaining profiles, as well as information on the supporting equipment and special techniques, were sought. The findings and conclusions of this report have been drawn from the analysis of operational characteristics in thirty-eight SDI services of the United States, and three SDI services of the United Kingdom; this represented a major portion of some fifty systems known to be in operation as of August 1967. The principal data collection and verification tools consisted of structured questionnaires, phone interviews, and published literature on specific SDI systems. To insure accuracy of data, all of the respondents were asked to review and comment on the first draft report. Their responses and critique are incorporated in this report. (Author/RM)